Noticing that your next door neighbor gives the local Synagogue twice as much per month as you do, might inspire you to up your game. Noticing that they give twice as much per month as you pay in rent might make you stop attending. And on the other side, very wealthy donors may be disinclined to give what they can afford because they don't want to embarrass their friends and neighbors, or do not wish to reveal just how wealthy they are. I suspect this is one reason many organizations that do publish donor lists include an option for donating anonymously.

I think this effect could be lessened by reporting one's donation in a percentage, rather than absolute value. Wealthier people could still afford more, but it wouldn't look as bad.

On some level, people would just have to realize that they can only do as much as they can, but it isn't out of the question to do more. I've seen some people on smaller incomes still manage to donate large percentages.